Generally, automatically shiftable vehicle transmissions of planetary design are already described in the art and are subject to continuous development and improvement. Such transmissions should feature a sufficient number of forward gears and one reverse gear and a transmission ratio that is very well-suited for motor vehicles with a high overall spread, favorable progressive ratio and a sufficiently large start-up transmission ratio for the specific application. In addition, this transmission should require low construction costs, in particular a low number of shift elements and, upon a sequential shifting operation, should avoid so-called “group gearshifts,” such that, when there are gearshifts to the next higher or next lower gear, only one previously engaged shift element is open, and one previously open shift element is engaged.
Such a multi-speed automatic transmission emerges, for example, from DE 10 2005 002 337 A1 of the applicant. It essentially comprises, inclusively, one drive shaft and one output shaft, a total of eight rotatable shafts, a total of four individual planetary gear sets and five shift elements. Through the selective engaging of three of five shift elements designed as clutches and brakes, a total of eight forward gears can be shifted without any group gearshifts.
A transmission diagram alternative to the 8-gear automatic transmission known from DE 10 2005 002 337 A1 is known from DE 10 2010 041 575 B3 of the applicant. Herein, a transmission with four individual planetary gear sets, five shift elements and a total of nine shafts is proposed, with which, compared to DE 10 2005 002 337 A1, the ring gear of the first planetary gear set arranged close to the drive is firmly connected to the transmission housing, and the sun gear of such first planetary gear set is connectable to the third shaft through the second shift element, which on its part can be fixed at the transmission housing through the first shift element.
A further development of the 8-gear automatic transmission known from DE 10 2005 002 337 A1 is known from DE 10 2009 001 253 B3 of the applicant. Here, through the addition of a sixth shift element formed as a clutch in the power flow between the drive shaft and the second planetary gear set that can be blocked through the engaging of the fifth of the previously present five shift elements, an additional forward gear can be represented, which, from its transmission ratio, is larger than the previous first gear of the 8-gear transmission, thus an additional start-up gear below the previous first gear of the 8-gear transmission.
A transmission diagram of a 10-gear automatic transmission is known from U.S. Pat. No. 8,545,362 B1, which conforms to this type and represents a further development of the 8-gear automatic transmission shown in FIG. 9 of DE 10 2005 002 337 A1. The modifications undertaken in U.S. Pat. No. 8,545,362 B1, compared to DE 10 2005 002 337 A1, concern the type and manner of the blocking of the second planetary gear set, which is neither constantly connected to the drive shaft or output shaft or directly connectable to the transmission housing. For this purpose, an additional sixth shift element is provided in U.S. Pat. No. 8,545,362 B1. As with DE 10 2005 002 337 A1, with U.S. Pat. No. 8,545,362 B1, the first planetary gear set is connectable to the transmission housing, the third planetary gear set is constantly connected to the output shaft and the fourth planetary gear set is constantly connected to the drive shaft. Thereby, the planetary gear carrier of the second planetary gear set forms the eighth shaft of the transmission, while the clutch shaft, which constantly connects the planetary gear carrier of the first planetary gear set to the ring gear of the third planetary gear set, forms the sixth shaft of the transmission. While, in FIG. 9 of DE 10 2005 002 337 A1, the eighth shaft is still constantly connected to both the fifth shift element provided for the blocking of the second planetary gear set and the fourth shift element leading to the sixth shaft, with U.S. Pat. No. 8,545,362 B1, the eighth shaft is separated from such two shift elements by the sixth shift element, which is an addition compared to DE 10 2005 002 337 A1. The additional sixth shift element is arranged in the power flow between the planetary gear carrier of the second planetary gear set and both the fourth and the fifth shift elements. As a result, the second planetary gear set can now be blocked through the simultaneous engaging of the fifth and sixth shift elements.